If I understand you correctly, the logit subroutine gets called at the code from different places, one line at a time. Thus, you need something like this (untested). I avoid the flipflop operator here, as it's somewhat confusing for me.

{
my $seentext;
sub logit {
    my($line) = @_;
    $line=~s/\0//g;
    $line=~/\S/ and $seentext = 1;
    print OUTF $line;
}
}
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